Riot police accompanied by armored vehicles, helicopters, bulldozers and a fixed-wing plane arrested protesters en masse and injured dozens, according to witnesses. The pipeline activists, self-dubbed “water protectors,” continued with prayer and ceremonial dance as they faced the line of police. Pictures circulating social media even showed an elder arrested as she prayed.

As smoke from burning barricades dissipated, protesters took to social media to share their message in the absence of widespread media coverage. Indigenous activist Harsha Walia tweeted that someone at the camp told her, "back to standoff. We are holding the line again. Police seem to be getting ready to snatch & grab particular ppl."

Dallas Goldtooth of the Indigenous Environmental Network said in a Facebook video shortly after the confrontation that a man contracted by the pipeline company tried to shoot an automatic rifle at water protectors as he crossed a barricade and jumped out of his car.

He said that water protectors, all unarmed, helped de-escalate the situation.

In another climactic moment, Goldtooth said that water protectors on horseback herded bison into the area, who were then pushed back by police shooting what may have been concussion grenades at the horses.

Others set fire to construction equipment, he said, and several tribal leaders were arrested.

“Nobody wanted this,” Morton County Sheriff Kyle Kirchmeier told media. He said that they were obligated to evacuate the protesters because they insisted on camping out on private property—which the water protectors maintained is 1851 Treaty Land.

“I can’t stress it enough: This is a public safety issue,” he said, pointing out that they burned tires and blocked highways. Police dismantled roadblocks during the raid.

A similar crackdown Saturday ended in the arrest of over 120 protesters and reporters.

The new Oceti Sakowin Camp was built to prepare for winter conditions, with thousands of Native Americans and allies still standing their ground against the construction of what will be the longest Bakken oil pipeline, running through four U.S. states. The pipeline’s route will pass through burial and ceremonial sites, leading tribes to reclaim their land guaranteed in an two federal treaties for the new camp. Construction continued nearby intermittently on Thursday.

Hundreds of Native American tribes have united to oppose construction, which they say violates U.S. protocol, treaties recognized by their nations and will contaminate the drinking water of millions downstream of the Missouri River.

Several lawsuits are pending against the project, which was approved by the U.S. Army Corps of Engineers.

Some of the police mobilized Thursday came from Hennepin County in Minnesota, which was the center of protests Tuesday for sending equipment to help evict campers. Hundreds gathered in downtown Minneapolis, whose city council passed a resolution opposing the pipeline.